Zwitterionic lipids such as phosphatidylcholine (PC) are major components of the membranes that compartmentalize organisms. Although there is a large literature on PC, cationic and non-ionic lipids, there are surprisingly few studies on modifications to dichain-lipids that retain a zwitterionic neutral head group at pH 7.4. Colleagues at the University of California, San Francisco, USA have developed two novel class of dichain zwitterionic lipids, namely the sulphobetaines (SB) and oxypropyl(dimethylammonio)acetates (PAA), that differ structurally from PC lipids in that the anionic sulfonate and carboxylate groups extend into the aqueous media while the cationic amine group is adjacent to the hydrophobic region. The present proposal aims to study the interesting salt-dependent properties of the vesicles formed by these novel lipids using SANS in combination with contrast variation.